Holding up banners that read, "Not here, Not anywhere" and "Stop plundering our oceans", Greenpeace activists took to the port in Valparaiso on Friday. Two activists also tried to board the 142 metre-long Margiris in order to stall her return to the South Pacific where she fishes on stocks that are in a perilous state.

Local Chilean fishermen, who have seen their own fish stocks plummet due to overfishing, supported our peaceful protest. Although the Margiris does not fish inside Chilean waters, she operates close enough to anger the local fishing community. Fishermen in the Valparaiso area have become desperate as they watch their government facilitate the operation of monster boats, like the Margiris, while not meeting their fishing needs. This desperation fueled some fishermen's frustration during Friday's protest, which unfortunately led some to take matters into their own hands. Peaceful non-violent direct action is at the core of all Greenpeace protests and this escalation meant that our activists had to disengage from the scene. Fortunately the protest reached a peaceful resolution.

I have been with Greenpeace for eight years now working with fishermen across the world. It saddens me that we have reached a point where average small-scale fisherman can no longer make a decent living. What I am witnessing is growing global opposition to the way decision-makers assist the worst offenders on our waters by subsidizing damaging activities, offering access to the most remote parts of our oceans and not having sufficient regulations in place. The victims are those who depend on healthy oceans for food and income, including you and me. The oceans belong to all of us.

Greenpeace has been following the Margiris for nearly two years, exposing her destructive practices wherever she goes. With her hefty nets spanning hundreds of metres, this vessel swallows up as much fish in a single haul as dozens of other, smaller boats collectively catch annually. Not only are fish captured, butthese nets also scoop up entire ecosystems: the fish, their predators – like sharks, manta rays and dolphins – as well as countless other marine life.

After contributing to the decimation of fish stocks in West African waters, this mammoth boat made its way to Australia in 2012 to continue its relentless pursuit of the world's remaining pelagic fish stocks. Together with a spectrum of people from fishermen to town mayors and politicians, my colleagues brought this vessel and its harmful ways to the attention of those on the highest political level inAustralia and successfully secured a two-year ban on all super trawlers including the Margiris.

While Australia's ban is a victory for our oceans, the problem doesn't end there. Fish stocks around the world are in serious trouble because there are simply too many boats chasing too few fish and not enough regulations to control them, particularly in international waters. Governments can and must change this by reducing their bloated fleets, starting with the monster boats.